In many processes in the chemical, food, and pharmaceutical industries, various separation techniques are used to isolate one material from another. Common techniques for separating solid materials from a liquid include vacuum or pressure filtration, drying, centrifugation, sedimentation and clarification. When a very pure solid product is required, separation may occur in multiple stages and may be combined with washing steps. For example, a solid recovered from one of the techniques noted above may be washed or reslurried with additional liquids in order to remove impurities before being subjected to another solid-liquid separation technique to recover a final, more pure product.
Multiple-stage separation techniques may result in higher purities of solid products, but may require substantially more investment in equipment. One highly successful method to reduce capital expenditures in a multi-stage separation is through the use of a rotary pressure filter apparatus. Rotary pressure filter apparatus have been designed to perform more than one of the steps of a multiple-stage separation technique in a single piece of equipment by progressing the material being processed through separate work zones. For example, known rotary pressure filter apparatus perform a filtration in a filter or feed zone to form a filter cake, followed by a washing of the filter cake in one or more wash zones. The washed filter cake may be dried in a drying zone before leaving the rotary pressure filter. Rotary pressure filter apparatus are generally known in the art and are disclosed, for example, in U.S. Pat. Nos. 2,741,369, 7,807,060 and US Pat. App. 20050051473.
Because the zones of the rotary pressure filter apparatus may be operated at different pressures, some rotary pressure filter apparatus have exhibited pressure fluctuations that have the potential to reduce the capacity of the rotary pressure filter apparatus and damage the filter elements therein.
Accordingly, there remains a need to improve rotary pressure filter apparatus to smooth pressure fluctuations.